Method and apparatus for air conditioning



C. H. CARR METHOD AND APPARATUS FOR AIR CONDITIONING Oct. 7, 1958 2 Sheets-Sheet 1 Filed Sept. 17, 1953 JNVENTOR. 6/660/27 h, 60m 3% Afro/Wen Oct. 7, 1958 c. H. CARR METHOD AND APPARATUS FOR AIR CONDITIONING Filed Sept. 17, 1953 2 Sheets-Sheet 2 "WWI INVENTOR. C/fffo/"a f7. Carr J (6 W ATTORNEK United States Patent O METHQD AND APPARATUS FOR AIR CONDITIONING (lliiford H. Carr, Kansas City, Mo.

Application September 17, 1953, Serial No. 380,822

4 Claims. (Cl. 98-38) This invention relates to air conditioning systems and more particularly to a method and apparatus for conditioning the air in a plurality of enclosures or zones from a central system.

In most large buildings, such as office buildings, hospitals, schools, hotels and the like, where the building is divided into a plurality of separate rooms, each of which is governed by different requirements so far as maintaining comfortable ventilation and temperature conditions is concerned, it has become an accepted practice to condition the air in the separate rooms through a combination system employing both a central system from which conditioned air is supplied to each room and local units which are stationed in each room to effect the final conditioning. Normally, the air supplied through the central or primary system is conditioned to some extent, and the purpose of the local units is to effect a secondary, or final, conditioning which provides the air in the room -with its design temperatures and properties.

In the primary-secondary systems referred to generally above, it is a conventional part of the operation to mix the primary air in relatively small proportions with recirculated air within each enclosure or room, such mixing taking place within each local unit, and at the same time effect a further sensible heating or cooling of the mixture according to the design requirements. This secondary treatment is normally accomplished through the use of suitable heat exchange means, such as a coil, to which is supplied a conditioning medium, for example, water. During summer operating conditions, that is, when cooling is desired, the water supplied to the local units is chilled while in the winter, heat can be added by circulating hot water therethrough. In most actual installations employing the primary-secondary system, the water is distributed to the local units from a second central station, the adjustments as to the quantity to be flowed through each coil being effected by suitable thermostatic-controlled valves at the particular unit in which it is contained. It will be understood, of course, that manual primary air control means are also positioned in each of the enclosures or zones to provide further flexibility.

The advantages to be obtained in the use of the primarysecondary system are so well known as to require little further exposition herein. However, there still remain many disadvantages which are inherent in the arrangement necessary for its successful operation. Foremost among these is the cost of installation, or first cost., It will be evident that in any system employing a twostage cooling or conditioning of the air, not only must provision be made for conducting the primary air from its central station, but also a system of pumps and conduits must be included for distributing the conditioning medium to the local units in which the secondary conditioning takes place. Many couplings and fittings must be utilized as well as a rather complex arrangement of valves and controls, all of which results in additional expense and increases the possibility of leakage when in operation.

An additional difficulty present in the primary-secondary, or two-stage systems, residesin the use. of separate coils in the individual units for the secondary'cooling. It will be understood by those versed in the art that unless the cooling medium is maintained at a temperature above the dew point of the air being passed'over the coil, condensation will take place on the surface of the coil, causing dirt to collect thereon with resultant clog,- ging, and also drainage means must be provided. This is very serious, more particularly where the latent heat load in the zone is relatively high, or in particularly humid climates. Obviously, this limits to a. consider.- able extent the amount of cooling that can be obtained. Moreover, during winter or in unusually cold climates, when the system is being utilized for heating, the failure to close a window in one of the rooms can result in freezing. of the coil and sometimes in disruption of the entire installation.

Other systems of air conditioning in which the secondary cooling is eliminated have been proposed, but in each the problem of water condensation on metal surfaces exposed to the cooled or conditioned air has made it necessary to keep the conditioned air at a temperature no less than approximately 20 F. lower than the room temperature. When the temperature of. thesupply air drops below that point, the temperature of the exposed metal surfaces drops below the dew point of the room air, causing moisture to condense out and drip from the surfaces.

It is a primary object of the present inventionto eliminate the above difficulties by providing a method and apparatus for conditioning air in a plurality of enclosures or zones from a central station without the use of a secondary conditioning phase or apparatus. In brief,

I employ a single central station for treatment of outside air, which, when properly conditioned, is distributed to the zones or enclosures where it is mixed in the desired proportions with recirculated air in the particular zone to obtain the desired comfort or design conditions. Through the adoption of my method and apparatus, the entire cooling, dehumidifying or heating load. is absorbed in the conditioning of what has been referred to above as the primary air, this air being mixed with. the recirculated air to arrive at the temperatures and humidity values which have been determined as desirable. No secondary heat exchangers are used or needed, thus eliminating entirely the flow system for the conditioning medium employed in existing installations, and its complex arrangement of pumps, motors, starters, and pipes.

It is a further object of my invention to provide an air conditioning system in which, by initially conditioning the incoming or make-up air to values outside the limits which had heretofore been thought possible, the room air can be brought to desirable comfort temperatures and moisture content at a comparable or lower operating cost than in known installations. This power saving is due to a variety of factors, including: (1.) by virtue of the lower temperatures given to the conditioned or supply air, less air is needed to bring the room down to comfort conditions, and I have actually found that the power required to operate the air fans is 50 percent less than in other systems of the type referred to earlier herein, representing a saving of approximately 5 percent in total power required; (2) secondly, no pumps are needed for circulating a secondary cooling medium through the building, an additional saving of 5 percent of total power required is gained; (3) the cooling of the outdoor air in my central plant is done in such fashion that it reduces the power consumption when compared with standard refrigeration apparatus by approximately 30 percent. Moreover, smaller size ducts can be utilized in the system, and the entire first cost is materially re- 'fication which takes place.

duced. In my system, only a single duct system is actually required for effective use, although, as will be pointed out in more detail hereinafter, it may be advantageous in certain installations to employ an exhaust return duct for added efficiency.

An important feature of my invention resides in taking cognizance of the three major variables which may be adjusted to reach a condition in the enclosure which is comfortable to the inhabitants, namely, temperature, humidity, and air motion. It is a familiar fact that for high temperatures, the wet-bulb temperature is of predominant importance in comfort considerations. For example, the American Society of Heating and Ventilating Engineers, after many years of research, has arrived at a series of tables and charts Which reflect what is termed -eifective temperature on the basis of known dry-bulb and wet-bulb temperatures and velocity of air motion. The term-effective temperature is used to designate any series of these conditions which produces the same degree of comfort upon the human body, and the tables which have been published by the Society (see Transactions, A. S. H. & V. E., 1927) show that an increase in dry-bulb temperature of the air can be adequately balanced to produce a comfort condition by either reducing the wet-bulb to a new value, or by increasing air motion, or by a combination of both. As an example, the same effective temperature, 73.6, can be produced with a dry-bulb of 84 F. and a wet-bulb of 62 F., or with a lower dry-bulb of 80 and a higher wet-bulb of 68, assuming a constant air velocity of 50 feet per minute.

"Similarly, the elfect of air motion may be obtained by increasing the velocity, with the concurrent raising of the wet-bulb or dry-bulb temperature without changing the etfective temperature.

In my invention, these factors and relationships play an important part. In particular, when my system is being employed for cooling, the air supplied from the central station constitutes the sole refrigeration or cooling medium for the room. This, of course, means that the conditioning or make-up air must be reduced to considerably lower moisture content and temperatures than is the case in the two-stage systems in use today. An adjunct of the cooling, or refrigeration of the make-up air to the low temperatures necessary, is the considerable dehumidi- Thus the make-up air, when mixed into the recirculated air in the room or enclosure, results in a very desirable reduction in the wet-bulb temperature which allows a higher dry-bulb temperature to exist while still producing a desirable effective tempera- 'ture.

The net effect of the extensive dehumidification is to offset the increased input necessary for the refrigeration of the make-up air to lower temperatures than now employed with the reduced load on the system re quired to take care of the sensible heat gain imposed by the lower differential between the inside and outside dry-bulb temperatures. Sincethe primary or conditioned air inmy system is considerably dryer than in other systems, it will be evident that dehumidification of the occupied space can be obtained with much less primary air, and thus the duct sizes and blowers are of smaller size than in other systems.

Coupled with the balanced refrigeration inherent in my system is the feature of providing means for obtaining a definite air motion in the enclosure or zone withdition within the room. With the jet pump arrangement, I am able to recirculate room air in proportions of from three to ten times the volume of the primary air.

A novel feature of my invention resides in the provision of a room unit in which the surfaces liable to come in contact with the relatively cold, conditioned air are also subjected to the counterflow of the room, or recirculated, air (which is of relatively high temperature) to maintain those surfaces at a temperature greater than the dew point of the air taken from the room. In this fashion the condensation of moisture on the surface of the unit is effectively prevented, eliminating the need for a drainage system and further reducing the cost of installation and operation.

A further object of my invention is to provide a system in which the air in one room is not recirculated to any other room in the buliding, but only in the particularroom itself. This is extremely important, particularly in the case of hotels and hospitals. Many building codes of various cities and states now include such a requirement.

Another object of the invention is to provide a system inwhich the exhaust air from the enclosures or zones can be utilized for heat exchange purposes at the central station, by which the operating power requirements for the system are reduced. 7

A further object is to provide control apparatus for governing the distribution of the conditioned make-up air to various zones and enclosures to bring about the desired comfort conditions.

Still another object is to provide a system which is simple and easy to operate; which can be installed at low cost and with a minimum of effort; and which has efiicient operation and great flexibility under a variety of conditions.

Other objects and advantages, together with the features of novelty appurtenant thereto, will appear in the course of the following description.

In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith, and in which like reference numerals indicate like parts in the various views:

Fig. 1 is a diagrammatic view illustrating an air conditioning system embodying my invention;

Fig. 2 is an enlarged longitudinal section through the thermostat for controlling the flow of make-up air to the individual mixing units; I

Fig. 3 is a front elevation of the room distribution unit, part being broken away for purposes of illustration;

Fig. 4 is a top plan view of the grill on the room unit;

Fig. 5 is a sectional view through the room unit and adjacent building structure taken along the line 5-5 of Fig. 3 in the direction of the arrows;

Fig. 6 is an exploded view showing the component parts of the grillwork, insulating material, and upper end of the venturi throat in the room unit; and

Fig. 7 is a cross section through the discharge nozzle.

Referring to the drawing, and more particularly to Fig. 1, reference numeral 10 indicates generally the casing of the conditioning plant which serves to condition outside air for delivery at a predetermined temperature and humidity to the duct system serving the building. The location of the plant may be at any suitable place within the building, preferably the basement, and conventional means (not shown) is provided for communicating outside air to the intake end of the plant, which is the end provided with louvers 11. At the other end of the casing is provided a blower 12, which serves to draw the outside air in through louvers 11, across the conditioning equipment positioned centrally in the casing, and to deliver it at a higher static pressure to the main supply duct 13 from which it is distributed to the various parts of the building, as will be described in detail at a later point in the specification. Suflice it to say at this point that in describing my system, it will be assumed that the building is divided for air conditioning purposes into a main division between east and West portions, which are served respectively by branch ducts 14 and 15 leading from the main duct 13; a plurality of subdivisions within each main division, each served by a riser duct 16 leading from the branch ducts 14 or 15, and for convenience denoted as zones; and a plurality of separate enclosures within each zone, for example rooms or ofiices, each of which contains a room unit within a casing 17 and through which the conditioned air is introduced into and thoroughly mixed with the air which is already in the enclosure to obtain the desired comfort conditions. The various branch ducts, risers, and room units are fitted with air flow control means for correctly distributing the output of the central plant 10 therethrough according to the heat load in the various parts of the building, and the nature and effect of their operation. will be made clear presently.

As has been mentioned earlier herein, the sole source for bringing about the desired comfort or process condition in the enclosures within the building is the air which is supplied from the central plant 10 through the duct system connecting with the enclosures. I have discovered that by conditioning the outside air passing through the central plant to a far greater degree than hitherto contemplated, and by utilizing relatively less quantities of this air, desired heat and humidity levels within the rooms can be obtained without requiring a secondary conditioning step at the room itself and without increasing the cost of operation of the system. However, under summer operating conditions, that is, where the heat gain in any enclosure must be offset by the introduction of air at a sufiiciently low temperature and humidity to bring the room condition down to the desired level, it is necessary to remove a far greater amount of heat and moisture from the outside air than can be accomplished in existing systems without unduly multiplying the expense of operation. To overcome this difficulty, and as a part of my broad concept of a single phase multi-duct air conditioning system, I have developed the arrangement illustrated in Fig. 1.

As previously described, the outside air is drawn into the casing it) through louvers 1i and passes through a conventional air filter 13 where any entrained dust, pollen and the like is removed. The filtered air then passes over a heat exchanger 19 and preheating coil 26, and through a bank of humidifying spray nozzles 21 in which the temperature of the water is controlled through a humidistat 22 which operates a valve 23. The water to the spray nozzles 22 is supplied from any convenient source, and steam to the preheat coil fro-m a steam main 24. The nature of operation of the heat exchanger 19 will be made clear presently.

Under summer operating conditions, the preheat coil 25) and spray nozzles 21 are normally inactive, and the air is passed into the refrigeration zone comprising the two banks of cooling coils 25 and 26 (and between the cooling coils, a bank of reheating coils 27), where it is subjected to cooling and dehumidification. The refrigeration medium for both of the cooling coils 25 and 26 is supplied through a liquor line 2% from a receiver 29 connected with a condenser 30. Each of coils 25 and 26 is provided with a separate return line, numbered respectively as 31 and 32, which make connection with separate compressor 33 and 34. Line 31 will henceforth be designated as the high suction line and line 32 as low suction. Conventional valves 35 and 36, respectively, control flow of the refrigerant through coils 25 and 26 under the control of thermostats 37 and 38 extending into the casing on the downstream side of the respective coils. The intermediate reheat coil 27 is connected with steam main 24, and is operated under control of a valve 41 which is governed by a humidistat 42 disposed within the casing at a point just ahead of blower 12.

The provision of separate return lines 31 and 32, which are subjected respectively to high and low suction pressures allows the rather extensive cooling of the outside air to be accomplished with a low power requirement. In essence, it amounts to a two-stage cooling; the air passing through coil 25 is cooled in a first stage from, for example l00 to 55 F., and the remaining cooling is done at the second coil 26 so that the final temperature is that desired, for example 25 F. Approximately onehalf of the refrigeration load is carried out at a relatively high temperature, with a high suction pressure in the return line 31, and the compressor 33 is thus handling a more dense refrigeration gas which permits more efiicient operation with less horse power required. The remaining one-half of the refrigeration load is carried out at the low suction pressure in line :22, tne gas in line 32 being less than in line 31 and thus requiring a compressor of greater power and displacement. it will be evident that if only one compressor were used, it would of necessity be required to operate at the low suction of line 32, and therefore that such operation would be extremely ineflicient so far as line 31 and coil 25 are concerned. In practice, using the two compressor method, the total power cost averages out at less than the power cost of operating a single compressor at the low suction condition.

It will be noted that after passing through compressors 33 and 34, the refrigerant is returned to a single condenser 34) which is connected by suitable flow lines with a conventional cooling tower 44. Once condensed and with its latent heat of vaporization gain incurred during the expansion cycle in the coils removed, the liquid refrigerant is returned to receiver 29.

A final heating coil 45 is located downstream from the last cooling coil 26, and is connected through a line 46 having valve 47 with the steam main 24*. Valve 47 is operated under the control of a thermostat 48 extending into the air stream on the downstream side of the heating coil 45.

Since my system is designed for both summer and winter air conditioning, it will be understood that when the air is being subjected to cooling and dehumidification (summer), the preheat coil 2%, spray nozzle 21 and final heating coil 45 will be inactive. These latter elements are employed under winter operating conditions when the air is being subjected to heating and humidification, at which time the cooling coils 25 and 2d are rendered inoperative. Under summer conditions, the outside air is cooled to a temperature range of from 0 to 49 F., with a concurrent reduction in moisture content; under winter conditions, the heating and humidification of the outside air can be controlled to conventional values well known to the art. The manner of heating and humidifying the outside air which I have provided is in itself Well-known in the art, and I malte no claim of invention as to the details of this particular phase of the system.

Following the treatment of the outside air in the central plant, it is delivered at a relatively high static pressure at an order of 1" to 4 by blower 12 to the main duct 13. In the illustrated embodiment, the main duct terminates in the two branch ducts 14 and 15 through which the air is distributed in desired quantities under the control of a swingable damper 49 hinged inside the ducts at the point of divergence. An electric or air-operated motor 50, familiar to those versed in the art, is connected with damper 49, and the damper can be adjusted thereby to control the relative flow to the ducts 14- and 15. As mentioned previously, in the illustrated embodiment duct 14 serves the east side of the building and duct 15 the West side. Under summer operating conditions, during the morning hours when the heat load on the east side exceeds that on the west, damper 49 is positioned to deliver a greater quantity of conditioned air to branch 14; in the afternoon, the damper is shifted to partially close duct 14, and to cause the bulk of the air to be delivered to branch 15 to compensate for the added heat load on the west side of the building. It will be understood that this operation can be made automatic by incorporating with motor a suitable timer mechanism, or alternatively, with a thermostatic control employing thermostats located at central points within the opposite sides of the building, or located on the roof and operated by the sun.

The risers 16, which connect with the branch ducts 14 and 15, are also fitted with control dampers 51 which are preferably operated by separate electric or air motors 52. Since, as explained previously, the risers 16 lead to separate zones within the building in which the heat load may vary, motors 52 are each connected with a thermostatic control 53 which is placed at a desirable central location within the zone. In this fashion a further preliminary quantitative distribution of the air is obtained, larger quantities being directed to those zones in which the heat load is heaviest.

The final distribution point for the conditioned air is at, of course, the individual rooms and enclosures within the zones. While I have shown only a portion of one such enclosure in the accompanying drawings, it will be understood that several enclosures are present in each zone and that each enclosure is provided with a room unit similar in construction to that indicated generally at 17, and described in more detail hereinafter.

The details of construction of a preferred embodiment of the room unit employed in my system are illustrated in Figs. 3 through 7, inclusive. In general, each unit comprises an outer, generally rectangular casing or cabinet 54, preferably formed of sheet metal, which is inset into one wall of the room. The conditioned air pipe 55 extends lengthwise within the bottom portion of the cabinet, and is covered throughout its length with a layer of thermal insulation material 56, such as a glass fiber mat. Spaced longitudinally along the upper surface of pipe 55 are a plurality of upwardly directed jets 57 each having disposed therein a partitioned stream straightener 57a and each also surrounded by the insulating material. Suspended from the top of the casing and aligned with each jet 57 is a venturi throat 58. The venturis 58 are also preferably formed from sheet metal, and throughout the major portion of their length are circular in cross section. As illustrated, each is provided with a flared lower end 5811 spaced above the terminus of its respective jet 57, and increases uniformly in diameter towards its upper end where it merges into a generally rectangular section 58b. The cross-sectional area of the rectangular section 58b, at its uppermost end, is equal to or slightly greater than the area of the venturi 58 at its point of greatest diameter.

As will be evident, the diameter of the jets 57 will vary somewhat in the individual units, the diameters increasing in size from the one nearest the point of connection of pipe 55 with its riser 16 to the most remote to ofiset the pressure gradient in the pipe. Also, if several units are connected with one riser, the diameters over-all may be varied from unit to unit on the same principle. This can be best accomplished by the use of orifice plates in the jets having apertures of the desired diameter.

As is particularly evident from Figs. 5 and 6, welded or otherwise secured to the section 53b of the venturi near its upper end and on opposite sides thereof are laterally projecting flanges 59. As shown in Fig. 5, these rest upon shoulders or ledges 60 and 61 respectively, extending inwardly from opposite sides of the casing and serve to suspend the venturi 58 within the casing 54. A rectangular filter pad 62 having a central aperture 59a therein is slipped over the end of the section 58b to rest on flanges 59. A grill section 63 of substantially equal size with filter pad 62 and also having a rectangular aperture centrally located therein rests on top of the filter pad 62.

The outlet of section 58b of the venturi 58 is covered by another grill 64 having a length greater than the length of the venturi outlet so that the ends thereof project across a portion of the grill section 63. The grill 64 is confined in the outlet between the upwardly projecting side walls 580 of the venturi outlet.

Completely surrounding the outher surface of each venturi unit 58 and spaced therefrom to provide an annular passageway is a secondary tube section 65 which is secured to the inside of the casing in any suitable fashion, such as by welds 66. As illustrated, the lower edge of the outer tube 65 is spaced above the flared portion 58a of the venturi 58, and the annular inlet to the tube is covered by the filter pad 62.

The nature of operation of the room unit in mixing the conditioned air with the room air and in attaining the desirable effective temperature in the room is believed fairly evident from the drawing. Under summer operating conditions, the air is supplied to the pipe 55 at a temperature in the order of 0 to 40 F. at a static pressure of approximately /2" water gauge. This cold air is discharged through the nozzles 57 in a jet-like stream which is directed axially into the flared lower end 58a of the venturi tube 58. As will be understood by those versed in the art, immediately upon discharge from the nozzle 57, the jet is subjected to a slight expansion; however, as it enters the section 5811 it is again constricted, increasing the jet velocity and reducing the pressure. This reduction in pressure causes the air surrounding the jet stream within the cabinet to be drawn into the venturi where it is thoroughly intermixed with the cold air. Concurrently a How from the room through the grill 63 and filter pad 62 downwardly through the annular passageway 64 is created, as illustrated by the arrows in Fig. 5. In effect, an annular counterflowing stream of air at the room temperature is brought into contact with the outside surface of the venturi 58 throughout a major portion of its length. The confining of the incoming or recirculated air from the room to a flow path along the venturi 58 insures that the temperature of the metal surface of the venturi will be maintained at a relatively high median and that, as a consequence, there will be little or no possibility of condensation of moisture on the surface of the venturi since the metal temperature will be maintained at a higher value than the dew point of the recirculated air. It will be evident that the external surfaces of the venturis 53 may be provided with projecting fins or the like to increase the metal surface area exposed -to the incoming room air.

The positive action of the jet and venturi arrangement in drawing room air into the unit and in creating a relatively high speed air stream discharging into the room is an important feature of my invention in that it makes possible the use of temperatures in the conditioned air heretofore unavailable. The problem of moisture condensation on the metal surfaces of the unit has been eliminated, and air motion within the room has been attained without the use of supplemental fans or blowers. When coupled with the inherent dryness of the relatively cold air being supplied to the unit, this positive air motion makes it possible to obtain an effective comfort temperature in the room at a much higher dry-bulb room temperature than in existing systems. Moreover, the positive intermixing obtained through the venturi arrangement, and the dry quality of the cold air, results in a room condition in which the wet-bulb temperature and relative humidity of the air has been considerably reduced.

The air flow through the pipe 55 is controlled by means of a butterfly valve or damper 67 positioned within the pipe near one end of the cabinet 54. The damper 67 is mounted on a rotatable shaft 68 extending through and journaled in the pipe 56. One end of the shaft 68 projects beyond the insulating covering 56 and has affixed thereto a radial arm 69 by which the butterfly is rotated to vary the air flow through the pipe under the control of the thermostatic control unit detailed in Fig. 2.

Referring to Fig. 2, the main body of the control unit comprises two cylindrical bellows units 70 and 71 of Conventional design which are sealed to a transverse partition plate 72. Each bellows has extending centrally from its exposed end a shaft, reference numerals 73 and 74 respectively, and an extending portion of the plate 72 has aflixed thereto a toothed rack 75. The rack 75 rides upon the meshes with a worm gear 76 at the end of a rotatable rod 77 extending through and journaled in the end wall of the casing 54 of the room unit. A turning knob 78 is provided on the outer end of rod 77 outside the casing, and it will be evident that the plate 72 with the connected bellows 7t) and 71 can be shifted longitudinally of the bellows axis in either direction by manipulating the knob 78.

The shaft 74 extending from bellows unit 71 rests in a trough-like ledge 79 secured to and extending inwardly from the inside wall of the cabinet or casing 54. The oppositely-directed shaft 73 on bellows 70 is telescopingly received in a tube-like member 80 which at its other end is secured to the free end of the radial arm 69 by means of a pin 81. As will be noted from the drawing, pin 81 rides in an elongated slot 69a formed in the flattened end of arm 69.

To link the bellows units 70 and 71 separately to tube 80, I have developed the following arrangement. Each of the bellows shafts 73 and 74 is provided with an enlarged peripheral flange 73a and 7411 having formed therein an annular groove. A similar flange 80a (also grooved) is formed on the end of tube 80. When it is desired to link the bellows 71 to the radial arm 69 so that the expansion and contraction of the bellows 71 will be transmitted to the arm 69 and the butterfly or damper 67, a U-shaped, relatively rigid link 82 is positioned with its ends respectively in the grooves of the flanges 80a and 74a and the ends of the link are secured therein in any suitable manner, such as by pins 83. It will be evident that while any movement of bellows 71 will be directly transmitted through the link 82 to arm 69 and will cause the damper to be adjusted accordingly, the opposite bellows 70 is free to expand and contract in a like manner without affecting the position of the damper since its shaft is freely slidable in the tube 80.

With the damper 67 so arranged in the air pipe 54 that clockwise movement of the arm 69 serves to open up the flow passage in the pipe, the bellows 71 serves as a summer bellows. In other words, as the temperature of the air surrounding the bellows 71 increases, the bellows will expand causing shaft 74 to move to the right and drawing with it the tube 80 through the link 82. This causes the damper to open slightly and permit a greater amount of cold air to pass to the jets 57 and to enter the room. As the air surrounding the bellows '71 is reduced in temperature, the bellows will contract, rotating the arm 69 in a counterclockwise condition to turn the damper toward its closed condition and decrease the supply of cold air to the room.

Exactly the opposite situation is true under winter operating conditions, when the air delivered through the pipe 54 is heated air. In the winter, link 82 is removed and substituted therefor is a shorter link 84 which connects bellows 70 (or the winter bellows) with the tube 80. The manner of connection of the link 84 with the flanges 73a and 80a is identical with that previously described. When so linked, the expansion and contraction of bellows 70 controls the damper 67 and bellows 71 (the summer bellows) is free to expand and contract without exercising any control over the air flow. When the temperature in the room rises above the pre-set level, bellows 70 expands thereby turning arm 69 counterclockwise and reducing the flow of heated air through the pipe. When the temperature in the room drops below the desired level, the concurrent contraction of bellows 70 draws the arm clockwise to open the damper further and increase the supply of hot air.

It will be understood that the preliminary setting of the damper 67 at a position to give a desired temperature within the room, either winter or summer, is made through adjustment of the knob 78. Thereafter, the bellows units 70 or '71 take over to maintain the temperature at the selected level in the manner hereinbefore described. The bellows units are located inside the cabinet where they are subjected to the temperature of the air being drawn from the room through the jet pump action of the venturis 58, and the control is based on the median temperature of the room air rather than on the temperature at any particular point in the room. It is well known that with thermostatic control positioned at a selected point in a room, considerable care must be taken to locate the control at a point which is not adversely affected by hot or cold air currents, and in many cases this presents an amost insurmountable problem.

A remaining feature of my invention resides in the utilization of the exhaust air from the various enclosures: of the building in the treatment of the incoming outside air at the central conditioning plant 10. Referring to Fig. 1, it will be noted that I have shown a series of exhaust ducts which terminate in a main exhaust duct 91 returning to the central plant. Duct 91 is provided with an exhaust fan 92 to draw the air from the various parts of the building, and a branch duct 93 which connects with the heat exchanger 19 located in the casing 16 of the central plant. A damper 94 is provided for controlling the air fl-ow through the heat exchanger 1.9.- It will be evident that in either the summer or winter, the exhaust air can be used to preliminarily withdraw or add heat to the incoming outside air before it passes into the main conditioning equipment, thereby reducing the power or heat required to bring the outside air to its final condition. In the summer, the exhaust air is cooler than the outside air, and when passed through the heat exchanger 19, reduces the temperature of the outside air before it enters the cooling coils. In winter, the exhaust air is warmer than the outside air, and as a result, the outside air is subjected to a preliminary warming prior to its passage through the main heating coils. In both cases, the utilization of the exhaust results in a power or heat saving of measurable value.

From the foregoing description, it will be seen that I have accomplished all of the objects set forth. By the use of conditioned air delivered at a temperature of 0 to 40 F., I have been able to reduce the size of the ducts and risers to a considerable extent. This has been accomplished also in large part by the provision of positive air flow means in the room units which intermix and discharge properly conditioned air into the room at increased velocities. I have also provided apparatus in which the problem of condensation on cold metal surfaces has been avoided, making it possible to utilize much lower temperatures in air conditioning systems than heretofore practical. The entire system is readily adaptable to a variety of conditions, both summer and winter, and provides a means for completely conditioning an entire building with a low installation cost and operating expenses.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, 1 claim:

1. A system for conditioning air in an enclosure comprising heat transfer means for altering the temperature and humidity of outside air, power and duct means for drawing the outside air through said heat transfer means and delivering the conditioned outside air to the vicinity of said enclosure, a discharge nozzle positioned within said enclosure and connected with said duct means through which said conditioned air is discharged in a high velocity stream, a venturi element axially aligned with said nozzle and open at both ends for communication with the air within said enclosure, and a casing enclosing said nozzle and venturi element and having an outlet through which said venturi element discharges to said enclosure, said casing being provided with an an nular inlet surrounding said venturi element at its dis charge end through which air from the enclosure is drawn into said casing and toward said nozzle and including means confining the passage of said air to a path adjacent, around the entire outside and over the full length of said venturi element.

2. A system as in claim 1 wherein the last named means comprises a tube element supported within said casing and concentric with and surrounding said venturi element and forming therewith an annular passageway communicating at one end with said inlet and opening at its other end within said casing.

3. A room air conditioning unit comprising a casing, an air supply pipe within said casing having a discharge nozzle, a venturi element supported within said casing and axially aligned with said nozzle, the outlet end of said venturi element being disposed centrally in an aperture in said casing having an area greater than the outlet end of said venturi element and forming an annular inlet through which air is drawn into said casing as air is discharged from said venturi element, and means surrounding said venturi element and confining the flow of said air drawn into the casing to a path adjacent, around and over the full length of said venturi element.

4. A room air conditioning unit as in claim 3 wherein the last named means comprises a tubular element sup- 12 ported within said casing and concentric with and surrounding said venturi element through a substantial portion of the length of said venturi element, said tubular unit forming an annular passageway around said venturi element communicating at one end with the annular inlet and open at its other end within the casing.

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